The present invention relates generally to opto-electronic transmitters or light sources. More particularly, the invention relates to optical transmitters referred to in the art as transmitter optical subassemblies (TOSAs) which can efficiently couple optical power from a solid state light source such as a light-emitting diode into an optical fiber coupled to the source.
Devices of this type are known which are connectorized, i.e., fitted to accept an optical fiber terminated with a standard fiber connector end terminal of the kind used in standard ST, SC, or similar connectors. Connectorization can insure that, when the properly terminated end of an optical fiber is connected to the device, the coupling of optical signals from the source into the fiber can be achieved repeatably and without unacceptable signal losses.
Transmitter optical subassemblies are known, for example, from U.S. Pat. No. 5,040,862. The subassemblies of this patent comprise several common elements disposed within a suitable enclosure, including a light-emitting diode such as a laser diode which can be modulated to generate an optical signal, and a light-focusing or convergent lens to focus the output from the light source as a source image at an optical coupling point corresponding to the endface of an optical fiber terminating within the enclosure.
The device of this patent further comprises an integral terminal connector member such as a receiving ferrule, adapted to receive and position the input end of a connectorized or otherwise suitably terminated optical fiber. The ferrule is positioned so that the fiber endface will be located at a position within the enclosure where maximum coupling of optical power into the end of the fiber can be provided.
While a variety of transmitter optical subassemblies of this type are known, most of the existing designs exhibit characteristics which significantly limit coupling efficiency and/or repeatability in use. For example, in all designs employing convergent lenses, temperature changes occurring during device operation can affect the refractive index, thickness, and radius of curvature of the lens elements. The result is a change in the location of the source image, i.e., the focal point or focal plane in which light from the light source is focused for coupling into the fiber.
In addition, the design of these devices is frequently such that minor alignment errors in the course of device assembly, such as small errors in the positioning of the solid state light source, lens, or connector end within the final assembly, can substantially affect the signal coupling efficiency of the device. This uneconomically decreases the select rate for the assembly process.
The art is also aware that these devices are subject to significant performance degradation when subjected to minor levels of applied mechanical stress in use. This places constraints on the design of optical systems employing the devices, in order to avoid mounting configurations wherein such stress might be encountered.
Finally, existing connectorized device designs have favored connector placement at locations which position the receiving ends of optical fibers connected thereto at points of maximum optical power coupling. The effect of such positioning is that very small changes in the position of the fiber end disadvantageously result in very large changes in the amount of optical power coupled into the fiber.
It is therefore a principal object of the present invention to provide a transmitter optical subassembly which is more resistant to temperature changes than the prior art devices, and to provide designs for such devices which render them less sensitive to applied mechanical stresses.
It is a further object of the invention to provide optical subassembly designs which reduce the harmful effects on device performance of minor rotational or translational misalignments in light source, lens and/or terminal components during device manufacture.
It is a further object of the invention to provide a design for a transmitter optical subassembly which exhibits reduced sensitivity to connected fiber positioning than prior art subassemblies.
It is a further object of the invention to provide a method for manufacturing a transmitter optical subassembly offering improved repeatability and precision in the production process.
Other objects and advantages of the invention will become apparent from the following description thereof.